Islamic State militants are committing systematic rape and sexual violence against Iraq's Yazidi minority, Human Rights Watch said Wednesday, in the latest report detailing alleged war crimes by the fighters in the 10 months since they stormed large areas of the country.

The Islamic State offensive included laying siege to the Mount Sinjar area, forcing thousands of Yazidis to flee while the militants kidnapped thousands and killed many others. Their tactics included dividing women and children from their families and moving them to other areas of Iraq and into Syria to be sold or married off to militants.

Human Rights Watch interviewed 20 women and girls from among the roughly 1,000 Yazidis that Kurdish authorities say have managed to escape. They described "a system of organized rape and sexual assault" with threats of beatings for those who resisted. Some who were not raped told the rights group that seeing the abuse of others, and the thought that they could be next, brought on "constant stress and anxiety."

Human Rights Watch said the women and girls spoke of trying to hang themselves or cutting their wrists with razors in attempts to commit suicide in order escape the abuses.

The rights group urged Islamic State fighters to release the civilians they still hold and to end forced marriages, rape and other sexual assaults. It also called for better medical care for the women and girls who do escape, particularly psychosocial support and efforts to educate people about how counseling can help.

"Yazidi women and girls who escaped ISIS still face enormous challenges and continuing trauma from their experience," said Liesl Gerntholtz, women's rights director at Human Rights Watch. "They need urgent help and support to recover their health and move on with their lives."

The abuses detailed in the Human Rights Watch report are similar to those that Amnesty International described in December after its own interviews with women and girls who escaped Islamic State custody. Amnesty said the militants used "rape as a weapon" against the Yazidis and did so openly in order to engender a brutal reputation to make others fear them.

The U.N.'s human rights chief released a report last month saying the Islamic State group seemed intent on eliminating the Yazidis entirely, with that genocide accounting for only part of potential war crimes and crimes against humanity that should be referred to the International Criminal Court.

The Islamic State siege of Mount Sinjar played a major role in bringing U.S. airstrikes to Iraq in a campaign that has expanded with a coalition of militaries to include bombings targeting the militants in Syria as well. The combined campaigns have included more than 3,200 airstrikes since August, and helped Iraqi forces retake some of the territory the militants once controlled.